1. Field of the Invention
Embodiments of the present invention relate generally to magnetic heads, disk drives, and methods and, in specific embodiments, to a head comprising a read element, a top read shield, a bottom read shield, a stray field shield, and an exchange decoupling layer, where the top read shield, the bottom read shield, and the stray field shield allow for at least partially shielding the read element from stray magnetic fields, and the exchange decoupling layer allows for at least partially providing exchange decoupling of the stray field shield and the bottom read shield.
2. Related Art
A major goal among many disk drive manufacturers is to continue to increase an amount of data that can be stored on a recording medium while still maintaining data integrity and disk drive reliability. In recent years, disk drive manufacturers have started to look to perpendicular recording as a way of increasing a number of data bits per square inch on a recording medium by storing magnetization vertically within the recording medium, rather than simply storing magnetization longitudinally in the recording medium as in longitudinal recording. However, experiments have shown that perpendicular disk drives are more sensitive to external stray magnetic fields than are longitudinal disk drives, and such external stray magnetic fields may lead to a loss of performance and even to irreversible disk drive failure in perpendicular disk drives.
Perpendicular disk drives typically comprise a head and a recording medium. The head typically comprises a read structure and a write structure, where the read structure typically comprises a read element for reading data from the recording medium and two read shields for at least partially shielding the read element from stray magnetic fields. It is generally desirable to have the read element react only to magnetic fields provided from a portion of the recording medium that is directly under the read element, so the read element may be placed between the two read shields, where the read shields are intended to block magnetic fields provided from neighboring portions of the recording medium.
Examples of perpendicular disk drives are provided in the following references: (i) U.S. Pat. No. 6,842,313 entitled “Floating Down Stream Perpendicular Write Head Shield”, the contents of which are incorporated by reference herein; (ii) U.S. Pat. No. 6,950,277 entitled “Concave Trailing Edge Write Pole for Perpendicular Recording”, the contents of which are incorporated by reference herein; and (iii) U.S. Pat. No. 6,760,191 entitled “Internal Heat Dissipater used to Reduce Slider and Write Pole Thermal Protrusion for Thin Film Recording Heads”, the contents of which are incorporated by reference herein.
Experiments have demonstrated that perpendicular disk drives are sensitive to external stray magnetic fields that are generated by sources external to the disk drives. External stray magnetic fields may be generated by many external sources including, but not limited to, motors, magnets, electric currents, and the like. For example, external stray magnetic fields entering a particular disk drive may be caused by drive motors of adjacent disk drives that are in a same enclosure with the particular disk drive. Also, with disk drives placed in televisions, automobiles, computers, and the like, there are many potential sources of external stray magnetic fields, such as power supplies, motors, electric circuits, and the like.
In various experiments, a loss or performance has been observed in perpendicular disk drives when they are operated in the presence of external stray magnetic fields. Such a loss of performance was noticed even for relatively small external stray magnetic fields. For example, in various experiments, one order of bit error rate (BER) loss was observed in perpendicular disk drives when the disk drives were in the presence of external stray magnetic fields with strengths even as small as 10 Oersted (Oe). A possible explanation of the BER loss is an increase in asymmetry of a read element due to a resulting stray magnetic field in a vicinity of the read element.
Also, in various experiments, an irreversible disk drive failure has been observed if a perpendicular disk drive is operated in the presence of a large enough external stray magnetic field. For example, irreversible disk drive failures have been observed in perpendicular disk drives that are operated in the presence of external stray magnetic fields with strengths even as small as approximately 50 Oe. The irreversible failures of the disk drives have been associated with an erasure of servo data on recording media in the disk drives. Servo data on a recording medium permits the determination of the position of a head with respect to the recording medium, and if the servo data is erased, the head is not able to be positioned properly for read and write operations, which leads to an irreversible drive failure.
Based on the experiments that show a loss of performance and even a possible irreversible disk drive failure for relatively small external stray magnetic fields, it is important to try to determine a possible explanation for the increase in asymmetry of a read element and an erasure of data on a recording medium due to such relatively small external stray magnetic fields. It has been noted in U.S. Pat. No. 6,995,950 entitled “Transverse Biased Shields for Perpendicular Recording to Reduce Stray Field Sensitivity”, the contents of which are incorporated by reference herein, that read shields capture stray magnetic fields. In an analysis performed by the first named inventor of the present patent application as filed, the read shields have been found to provide a large magnetic field when in the presence of an external stray magnetic field, which can explain the increase in asymmetry of a read element and the erasure of a recording medium.
Traditional read shields are manufactured with thicknesses that are designed to provide good domain structures such that the creation of bad magnetic domains in the read shields can be hopefully avoided. However, the first named inventor of the present patent application as filed has determined that the geometries of traditional read shields cause the read shields to capture, focus, and greatly magnify external stray magnetic fields, which can lead to strong magnetic fields near a read element and a recording medium in a disk drive to possibly result in a loss of performance in the disk drive and an irreversible drive failure in the disk drive.
In light of the above-mentioned problems, there is a need for read shields of heads of disk drives that provide for less magnification of external stray magnetic fields than with traditional read shields. Also, there is a need for reducing a sensitivity of disk drives to external stray magnetic fields without greatly increasing a number of manufacturing steps or a manufacturing cost.